Execute, Requery, and Clear Methods Example (VJ++)

This example demonstrates the Execute method when run from both a Command object and a Connection object. It also uses the Requery method to retrieve current data in a recordset, and the Clear method to clear the contents of the Errors collection. The ExecuteCommand and PrintOutput procedures are required for this procedure to run.

// BeginExecuteJ
// The WFC class includes the ADO objects.
import com.ms.wfc.data.*;
import java.io.*;

public class ExecuteX
{
   // Main Function

   public static void main (String[] args)
   {
      ExecuteX();
   }

   // ExecuteX Function

   static void ExecuteX()
   {
      // Define string variables.
      String strSQLChange = "UPDATE Titles SET Type = "
            + "'self_help' WHERE Type = 'psychology'";
      String strSQLRestore = "UPDATE Titles SET Type = "
            + "'psychology' WHERE Type = 'self_help'";
      String strCnn = "Provider='sqloledb';Data Source='MySqlServer';"
            + "Initial Catalog='Pubs';Integrated Security='SSPI';";

      // Define ADO objects.
      Connection  cnConn1    = null;
      Command  cmdChange  = null;
      Recordset  rsTitles  = null;

      try
      {
         // Open connection.
         cnConn1 = new Connection ();
         cnConn1.open(strCnn, "", "", AdoEnums.CommandType.UNSPECIFIED);

         // Create command object.
         cmdChange = new Command();
         cmdChange.setActiveConnection (cnConn1);
         cmdChange.setCommandText (strSQLChange);

         // Open recordset with Titles table.
         rsTitles = new Recordset();
         rsTitles.open("Titles", cnConn1,
                    AdoEnums.CursorType.STATIC,
                    AdoEnums.LockType.OPTIMISTIC,
                    AdoEnums.CommandType.TABLE);

         // Print report of original data.
         System.out.println("\n\n\tData in Titles table "
                        + "before executing the query: \n");
         PrintOutput(rsTitles);

         // Clear extraneous errors from the Errors collection.
         cnConn1.getErrors().clear();

         // Call the ExecuteCommand subroutine to
         // execute cmdChange command.
         ExecuteCommand(cmdChange, rsTitles);

         // Print report of new data.
         System.out.println("\n\n\tData in Titles table after "
            + "executing the query: \n");
         PrintOutput(rsTitles);

         // Use the Connection object's execute method to
         // execute SQL statement to restore data.
         cnConn1.execute(strSQLRestore);

         // Print report of restored data.
         System.out.println("\n\n\tData after executing the query "
            + "to restore the original information: \n");
         PrintOutput(rsTitles);
      }  // End Try statement.
      catch( AdoException ae )
      {
         // Notify user of any errors that result from ADO.

         // As passing a Recordset, check for null pointer first.
         if (rsTitles != null)
         {
            PrintProviderError(rsTitles.getActiveConnection());
         }
         else
         {
            System.out.println("Exception: " + ae.getMessage());
         }
      }   
      
      finally
      {
         // Cleanup objects before exit.   
         if (rsTitles != null)
            if (rsTitles.getState() == 1)
               rsTitles.close();   
         if (cnConn1 != null)
            if (cnConn1.getState() == 1)
               cnConn1.close();
      }
   }

   // ExecuteCommand Function

   static void ExecuteCommand(Command cmdTemp, Recordset rstTemp)
   {
      try
      {
         // CommandText property already set before function was called.
         cmdTemp.setCommandType(AdoEnums.CommandType.TEXT);
         cmdTemp.execute();

         // Retrieve the current data by requerying the recordset.
         rstTemp.requery(AdoEnums.CommandType.UNKNOWN);
      }
      catch( AdoException ae )
      {
         // Notify user of any errors that result from ADO.
         PrintProviderError(rstTemp.getActiveConnection());
      }
   }

   //  PrintOutput Function

   static void PrintOutput(Recordset rstTemp)
   {
      // Declarations.
      BufferedReader in = new 
         BufferedReader(new InputStreamReader(System.in));

      // Ensure at top of recordset.
      rstTemp.moveFirst();

      // If EOF is true, then no data and skip print loop.
      if( rstTemp.getEOF() )
      {
         System.out.println("\tRecordset empty\n");
      }
      else
      {
         // Enumerate Recordset and print data from each.
         while( !(rstTemp.getEOF()) )
         {
            // Convert variant string to convertable string type.
            System.out.println("\t"
               + rstTemp.getFields().getItem("Title").getValue() + " "
               + rstTemp.getFields().getItem("Type").getValue() + "\n");
            rstTemp.moveNext();
         }
      }
      try
      {
         System.out.println("\nPress <Enter> key to continue.");
         in.readLine();
      }
      // System read requires this catch.
      catch( java.io.IOException je)
      {
         PrintIOError(je);
      }
   }

   // PrintProviderError Function

   static void PrintProviderError( Connection Cnn1 )
   {
      // Print Provider errors from Connection object.
      // ErrItem is an item object in the Connection’s Errors collection.
      com.ms.wfc.data.Error  ErrItem = null;
      long nCount = 0;
      int  i      = 0;

      nCount = Cnn1.getErrors().getCount();

      // If there are any errors in the collection, print them.
      if( nCount > 0);
      {
         // Collection ranges from 0 to nCount - 1
         for (i = 0; i< nCount; i++)
         {
            ErrItem = Cnn1.getErrors().getItem(i);
            System.out.println("\t Error number: " + ErrItem.getNumber()
               + "\t" + ErrItem.getDescription() );
         }
      }

   }

   // PrintIOError Function

   static void PrintIOError( java.io.IOException je)
   {
      System.out.println("Error \n");
      System.out.println("\tSource = " + je.getClass() + "\n");
      System.out.println("\tDescription = " + je.getMessage() + "\n");
   }
}
// EndExecuteJ

See Also

Clear Method | Command Object | Connection Object | Errors Collection | Execute Method (ADO Command) | Execute Method (ADO Connection) | Requery Method